Helen Boaden: the former BBC director of news has said the corporation had a 'deep liberal bias' in its coverage of immigration when she took up her role in 2004. Photograph: Jeff Overs/BBC/PA

Helen Boaden, the BBC's former news director, has admitted the corporation held a "deep liberal bias" in its coverage of immigation when she took up the role in 2004.

Boaden, who is now the BBC's head of radio, made the candid admission to a BBC Trust review into the impartiality of the corporation's coverage of immigration, religion and the European Union.

She told the review, published on Wednesday, that the BBC did not take the views of lobby group Migration Watch "as seriously as it might have" when she became director of news in September 2004.

Boaden is the latest BBC executive to state publicly that the corporation had a liberal bias on controversial topics such as immigration – an accusation it routinely faces from rightwing sections of the media.

Ceri Thomas, the acting deputy director of BBC News and former Today editor, was more measured when asked about the BBC's coverage. He told the review: "Any culture can be at risk of excluding what it thinks is wrong, possibly marginalising significant chunks of public opinion. We need to push against this consensus every day."

The frank remarks were included in a 67-page report by the BBC Trust which concluded overall that the BBC reflects a broad range of voices on immigration.

However, it said the BBC had been "slow to reflect the weight of concern in the wider community" about issues around the topic and must do more to seek out opinions "which 'people like us' may find unpalatable".

Stuart Prebble, the former ITV chief executive who carried out the review for the BBC Trust, said: "I have been impressed by the commitment of the BBC's journalists to ensuring that they bring a diversity of voices and viewpoints on a wide range of news stories to audiences across the country".

In the report, the trust urged the BBC to urged to avoid an "over-reliance on Westminster voices" after concluding that national politicians "tend to dominate" the views seen and heard on BBC programmes.

"It is also clear that the BBC cannot afford to rest on its laurels and it should ensure it does all it can to keep up with the ebb and flow of public opinion," said Prebble. "Which means avoiding over-reliance on Westminster voices, making efforts to find new voices even if they are contentious, and challenging their own assumptions on the accepted consensus."

In a press briefing, Prebble added that the BBC had "caught up and more recently improved" the amount of airtime it gives to views on immigration from outside the political elite.

Asked about criticism of the BBC for allowing controversial figures, such as the redical cleric Anjem Choudary, to broadcast their opinion, he added: "The BBC has an important role to play in hearing the voices we don't like the sound of and should keep its nerves when attacked by people who don't like to learn the lessons of history."

The report contained some implied criticism of Newsnight's Jeremy Paxman and Radio 4 Today presenters for their robust questioning technique. He said interviewees on the shows must seem like they are playing in a contest on "anything but a level playing field".

The result, he added, is that tuning into the shows "can be like witnessing what seems to be a big and healthy-looking bloke getting into the ring with the fairground prizefighter. One is perfectly fit and looks as though he could take care of himself, but the other does it for a living; one has been schooled in the Queensberry rules, and the other is a pugilist."

Prebble warned of the dangers of the BBC gathering too many of its journalists in its new Broadcasting House headquarters in London's West End, saying: "A large group of people working together are in danger of becoming more homogenous in their thinking, not less, and so less able to see when the output reflects a narrow outlook."

A BBC spokeswoman said: "We are pleased our coverage has been deemed 'remarkable' and 'impressive'.

"Stuart Prebble has concluded, overall, that our coverage of immigration is 'broad and impressive', that on the EU we offer 'a wide and comprehensive range of information and viewpoints' and that the BBC's coverage of religion is 'comprehensive and impressive'. He also states that the overwhelming number of journalists within the BBC leave their personal politics at home.

"However, the report provides some interesting insights. We agree it is always vital to guard against unconscious bias or 'group think' and will continue to do so and we've committed to a number of actions to improve our coverage even further."

The review cost licence-fee payers £175,000, the trust said, compared with the £200,000 spent on last year's examination of the BBC's Arab Spring coverage.

It is the fifth impartiality review by the BBC Trust, the corporation's governing body, and follows an internal 2007 report that described a "largely unconscious self-censorship" that led to certain opinions being routinely under-represented.

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